1. Field of the Invention
This invention pertains to a process for decreasing the content of chlorine in chlorinated hydrocarbons.
2. Description of the Related Art
Various chlorinated hydrocarbons such as polychlorinated biphenyls, tetrachloroethylene, trichloroethylene, 1,2,3-trichloropropane, polychlorinated naphthalene, chlorine containing fluorocarbons ("Freons"), polychlorinated cyclodienes such as aldrin and dieldrin, polychlorinated bicycloalkanes such as mirex etc., are recognized environmental contaminants. Numerous chemical, physical, and microbiological methods for eliminating these presently are under investigation. While microbiological techniques are useful in bioremediation of many contaminants, such techniques have not proven satisfactory for highly chlorinated products such as those containing four or more chlorine atoms; see e.g., Hill et al., Appl. Biochem. Biotechnol., 20/21, 233 (1989) and Waid, "PCBs and the Environment," Vol. II, 78, CRC Press, Boca Raton, Fla.
Various chemical approaches have been investigated but again it appears the greater the number of chlorine atoms in a target contaminant, the more difficult the dechlorination. Moreover systems which appear to be useful in the controlled environment of the laboratory encounter unexpected difficulties when an attempt is made to adapt the system to the competitive and ambient environment where such highly chlorinated products pose the greatest problem.
Wilwerding, U.S. Pat. No. 4,931,167, describes the degradation of polychlorinated biphenyls in a non-aqueous medium using anhydrous metal halides such as the chlorides and bromides of aluminum, titanium, tin, iron, etc.
Imamura et al., U.S. Pat. No. 4,957,717, describe the disposal of organic compounds by burning them in contact with a catalyst of a composite oxides such as titanium-silicon composite oxides and titanium-silicon-zirconium composite oxides.
Anderson et al., U.S. Pat. No. 5,035,784, describe degradation of polychlorinated biphenyls by photocatalysis by ultraviolet light utilizing porous titanium ceramic membranes.
Meunier, J. Organometal. Chem, 204 (1981), 345-346 describes the selective reduction of aromatic iodides with sodium borohydride activated by a catalytic amount of bis- (.eta..sup.5 -cyclopentadienyl)titanium dichloride or .eta..sup.5 -cyclopentadienyltitanium trichloride in dimethylformamide and in the presence of air. Aromatic chlorine atoms were not affected.
Kozloski, J. Chromatogr., 318 (1985) 211-219 describes partial catalytic dechlorination of polychlorinated biphenyls with sodium borohydride and nickel boride catalyst.
Stojkovski et al., J. Chem. Tech. Biotechnol. 1990. 51, 407-417, describe dechlorination of polychlorinated biphenyls and polychlorinated naphthalenes with nickel chloride/sodium borohydride catalysts. In a companion paper, J. Chem. Tech. Biotechnol., 1991, 51, 419-431, Stojkovski et al. extend the use of this nickel chloride/sodium borohydride system to chlorinated cyclodiene and bicyclic insecticides.
Bosin et al., Tetrahedron Letters, 4699-4650 (1973) report on the reduction of aryl halides with a sodium boro- hydride-palladium system.
Carfagna et al., J. Mol. Cat. 57 (1989) 23-28, describe the use of magnesium hydride and various metal halides in the reduction of aryl monohalides.
Rolla, J. Org. Chem., 46, 3909-3911 (1981) reports on the use of sodium borohydride to reduce a variety of halogenated hydrocarbons using hexadecyltributylphosphonium bromide as a catalyst.
Bergbreiter et al., J. Org. Chem., 54, 5138-5141 (1989) describe the use of tin catalyst attached to soluble polyethylene and polystyrene for use in alkyl halide reductions.
Loubinoux et al., Tetrahedron Letters, 3951-3954 (1977) report on the activation of sodium hydride by certain metal salts in the reduction of various organic halides.
Tabaei et al., Tetrahedron Letters, 2727-2730 (1991) describe the use of polyethylene glycol or tetraethylene glycol in the metal catalyzed reduction of chlorinated hydrocarbons with sodium borohydride or sodium alkoxyborohydride.